Confessions of a Shopping Trolley Wally
by Andy Foad G0FTD

Some time back in the beginning of 2005 I hatched a devious plan to get a decent signal out on HF using a shopping trolley.

The advantage was that I could easily take a 10 minute walk to the beach where I'd be able to have the massive advantage of nature's best linear amplifier called the sea.

It seems to add at least 20db when compared to nature's best attenuator - a typical suburban plot with poor earth conductivity and all that bricks and mortar adding insult to injury with those low angle signals.

Full view of the shopping trolly system

Figure 1 shows my trolley system in full view at my usual operating QTH at Whitstable, Kent.
I usually sit on the breakwater beam which acts as seat come workbench whilst providing a useful windbreak - assuming it's not a northerly
wind ! The sandy part on the left of the picture shows the high water mark.

Fig 2 Close-up view of the system

Figure 2 shows a closer view of the basic design whilst [Fig 3] shows in more detail the antenna mounting arrangements

Usually the 21ft vertical which is made from an old cb antenna with it's 27Mhz matching coil bypassed (I just removed it and replaced it with a wire link from the SO239 socket to the vertical section).

A short length of coax connects the vertical to an LDG Z100 auto tuner as shown in [FIG 4].

Fig 3 Antenna mounting and connections

Two 9ft wire radials are connected by a banana plug socket mounted just below the antenna and this allows the system to tune 5Mhz - 30Mhz and perform excellently on ALL bands.

Yes, even at 5Mhz I use only 9ft of radials as this appears to enhance some of the higher angle of radiation that comes from the antenna and on air tests using two quarter wave wire radials confirms this.

A short length of coax connects the vertical to an LDG Z100 auto tuner

Also a model using a NEC2 based antenna modelling program confirms that there will be a bit more high angle radiation.

However as is inherent with verticals (especially ones placed by sea water) there isn't that much high angle radiation to start with !

Great for dx but not really what you want if you're using the LF bands for local chats. Despite this I have been doing tests on 160/80/60/40m and working local stuff around the UK and europe more than adequately and often outperforming a local hams G5RV on 80/40m

On the HF bands I can work mobiles in California who are 5/9 +20db both ways and yet my friend's G5RV can't hear a thing.

At the same there is also a 200pf variable across the feedpoint and there is a good reason for this.

On some bands the auto atu fails to tune the antenna or will only have within it's fixed values to use values of L or C that will only provide a (for example) a 2:1 SWR so a quick tweak of the variable capacitor will allow the feedpoint impedance to come into range.

Now the large tapped inductance that can be seen on the left of Fig 3 is only put in series with the vertical element for operation on 160m/80m.

The auto atu isn't used because now the variable capacitor and the tapped inductance form a simple L-network which tunes the antenna on it's own when combined with the two 60ft wire radials which are used on these bands.

The taps and connections are made using simple banana plug leads and happilly fit into a SO239 socket by themselves.

There is also another trick that this antenna will perform for us on 6m.

For 6m operation the vertical element is collapsed down to about 1.5m, a quarter wave on 50Mhz and the other half of the dipole is the shopping trolley frame itself. The capacitance between the first 12 inches of the vertical and
it's U-bracket just so happens to be approx 60pf - which at 50Mhz produces a reactance of 50 ohms across the terminals ! An extremely effcient and free matching system for what looks like a vertical dipole in the shopping trolley system.

Now the minimum capacitance of the variable capacitor is only a few pF which mean a small tweak of the variable capacacitor will alter the reactance across the feedpoint to be 50 ohms where ever we desire on the 50Mhz band - neat eh ?

(The auto atu is not used on 6m).

This means I can work all bands from 160m - 6m and put a butt kicking signal out on all of them - if I can hear it then I can work it.

This contraption has worked the world with complete ease.

Fig 6 World War 2 CW key

FIG 6 shows the original army issued World War 2 key that I use for cw work which straps to my leg and came from a Wireless Set 18.
It was given to me as a gift from an old friend of mine who's name is quite apt - C.W. Field. Nice one Cyril !

I have also installed the 250Hz narrow filter for serious CW work.

The wire radials are stored on a crab fishing line thingy that can be purchased for a pound each with hook, line and sinker from..erm..the local "Poundshop".

The two 9ft wire radials have automotive bullet connecters on their ends to allow the additional radial wires to be added for low frequency operation.

You will also notice on the LDG auto atu there are two Icom stick on microphone holders which are used to hook over the IC-706 bail stand to provide the mounting of the atu to the bottom of the rig. It's a cheap and non destructive way of
mounting the atu.

The position of the clips may appear a bit odd being off centre, however when the rig's bail stand is in it's "not being used" position the atu becomes mounted in a mechanically "balanced" fashion.

At the bottom of the trolley is a 44 amp-hour lead acid battery which can be purchased locally for £27 each. Tests have proven that I can run 100w for about 5 to 6 hours before I have to go QRT - more than long enough for a
few hours out.

I have considered sealed "gel cells" but so far the I feel the higher cost doesn't justify using one when compared to a cheap vehicle battery, which I have found to be quite safe in transit even when tipped over.

Just make sure you don't tip them enough to redistribute the electrolyte around the other cells otherwise you may well lose capacity.

NOTE
Remember that matching coil removed from the CB original antenna ?

The view to North America from Whitstable in Kent as the RF flies, on a November evening

Well don't throw it away because attach a coax feed and 18ft of wire and you can have a 28Mhz end fed sloper antenna for free. With mine I hid the matching coil under the gutter and led the 18ft wire at 45 degrees and tied it off to a tree !
(You could even dangle it out of a balcony for a 10m antenna.)

Have fun getting off YOUR trolley -

73 de Andy G0FTD

(c) G0FTD 2005